This researrch is directed to the development of methods of growing single crystals of complex fluoride materials based on EuMgF4, whose remarkable photoluminescent properties have been described in a publication from this laboratory. Preliminary studies have shown that these materials also fluoresce intensely under X-ray excitation. It is proposed to prepare solid solutions of up to 75 mole% EuMgF4 in BaMgF4 and develop methods for the growth of single crystals ofsuch solid solutions. The fluorescense is due to the excitation of the Eu2+ ion and peaks in the blue region of the spectrum at about 440nm. Maximum efficiency is at 75 mole% EuMgF4, providing a high capture cross-section for x-radiation. Preliminary crystal growth studies will be done on the isomorphous system BaMgF4-SrMgF4. When crystals are available, studies of their sensitivity to X-ray excitation will be carried out. Photoluminescence studies and measurement of other physical properties over a range of temperatures will be made to assist our understanding of the physical processes in the crystals. The development of crystals of this type will be very useful for such applications of X-rays at CAT scanners, array devices, etc., because the high X-ray absorption and the high concentration of luminescent ions permit the use of very small crystals for improved resolution. The chemical nature of these insoluble fluorides avoids the hygroscopic nature of most present scintillation crystals. Some attempts to couple the luminescent output to photoconductive cells such as CdS will be made as a prototype of a miniature solid-state detector suitable for use in diagnostic devices such as CAT scanners.